Advances in polymerization and catalysis have resulted in the ability to produce many new polymers having improved physical and chemical properties useful in a wide variety of superior products and applications. The development of new catalysts has greatly expanded the choice of polymerization processes (solution, slurry, high pressure or gas phase) for producing a particular polymer. Also, advances in polymerization technology have provided more efficient, highly productive and economically enhanced processes. Especially illustrative of these advances is the development of the technology field utilizing metallocene catalyst systems.
As with any new technology field, particularly in the polyolefins industry, a small savings in cost often determines whether a commercial endeavor is even feasible. This aspect of the metallocene technology field is evident by the number of participants in the industry seeking new ways to reduce cost. In particular, there has been tremendous focus in the industry on developing new and improved metallocene catalyst systems. Some have focused on designing the catalyst systems to produce new polymers, others on improved operability, and many more on improving catalyst productivity. The productivity of a catalyst, that is, the amount of polymer produced per gram of the catalyst per hour, usually is the key economic factor that can make or break a new commercial development in the polyolefins industry.
From the early stages in the metallocene technology field, beginning with the discovery of the utility of alumoxane as a cocatalyst in the early 1980's, to the discovery of substitutions on the ligands of the metallocene compounds, through the development of non-coordinating anions, and today with the ever-increasing number of new metallocene compounds, catalyst productivity has been a primary focus.
A need still exists for higher productivity catalyst systems capable of providing the efficiencies necessary for implementing commercial polyolefin processes. Further, it has been found that conventional olefin polymerization processes that employ catalyst systems that use methylalumoxane as an activator often fail to efficiently utilize all the methylalumoxane present in the catalyst system. This is problematic because methylalumoxane represents a significant cost factor in the catalyst system. Thus, it would be highly advantageous to have a polymerization process and catalyst system capable of producing polyolefins with improved catalyst productivities and improved methylalumoxane efficiency.